Operators of mobile systems, such as Universal Mobile Telecommunications Systems (UMTS) and its offspring including Long Term Evolution (LTE) and LTE-Advanced, are increasingly relying on wireless small cell radio access networks (RANs) in order to deploy indoor (as well as dense outdoor) voice and data services to enterprises and other customers. Such small cell RANs typically utilize multiple-access technologies capable of supporting communications with multiple users using radio frequency (RF) signals and sharing available system resources such as bandwidth and transmit power.
Deployment of a large number of small cells can improve system-wide capacity in an area by providing cell-splitting gains. However, these systems result in unique challenges to a RAN operator. Users at cell edges often suffer from inter-cell interference since the received signal power from the serving cell is at the same level or even below the level of the received aggregated interference power from the adjacent cells. If the inter-cell interference is not well-handled, the capacity benefits from the small cell deployments could come at the cost of reliability and the general stability of the system. Reliability and stability of a RAN are often captured by an extensive set of Key Performance Indicators (KPIs) that essentially characterize the user experience in such a network. Unlike the deployments of macro cell networks, the deployments of small cell are more irregular in geometry. The shapes and sizes of the coverage areas of small cells can vary greatly. In addition, the load distribution between small cells is more asymmetric when compared with that of macro cells, which cover much larger areas. These impose significant challenges for managing small cell inter-cell interference and require techniques to take all the irregularities in geometry and load distribution into consideration as part of the small cell network design. Specifically this means interference management schemes need to be designed differently. Some key focus areas for the design are i) scalability (can support large number of small cells) and ii) stability (autonomously account for different performance requirements/network conditions)
There are several approaches that may be used to reduce the influence of inter-cell interference. For example, one approach is to employ a frequency reuse pattern and by that, avoiding usage of the same frequency bands at adjacent cells. A drawback of this approach is that only a small fraction of the frequency resources (equal to the reuse factor) may be used in each cell, while preferably one would like to reuse a significant part of the whole available frequency spectrum within every cell. Another approach to improve the spectral efficiency in cellular systems is a “fractional frequency” approach, which divides the frequency resource into two parts or more. The first part is used for the edge of cell regions, while the second part is used for the regions closer to the radio node. The first part is used with a designated reuse factor, appropriate for the cell edges where users are more vulnerable to interference due to their reduced signal power. The second part (covering the inner part of the cell), however, can be used with a higher reuse factor because the Signal to Interference and Noise Ratio (SINR) is higher in this part of the cell in view of both the stronger desired signal and the larger distance from the interferers. An example of such approach, for example is to divide the available channels into 4 channels, three of which are used in a reuse-3 pattern for covering the cell edge regions, while the fourth channel is used in a reuse-1 manner for the inner regions of the cells.
Despite the use of the well-known aforementioned techniques for reducing inter-cell interference, additional improvements in cell-edge user performance are desirable, particularly when small cells are employed.
This Background is provided to introduce a brief context for the Summary and Detailed Description that follow. This Background is not intended to be an aid in determining the scope of the claimed subject matter nor be viewed as limiting the claimed subject matter to implementations that solve any or all of the disadvantages or problems presented above.